Process for anhydrous calcium 12-hydroxy stearate and estolide containing grease



United States Patent PROCESS FOR ANHYDROUS CALCIUM 12-HY- DROXY STEARATEAND ESTOLIDE CONTAIN- ING GREASE John P. Dilworth, Fishkill, N. Y.,Charles H. Culnane, Jr., Wyandotte, Mich, and Roy F. Nelson, PortArthur, Tex., assignors to The Texas Company, New York, N. Y., acorporation of Delaware No Drawing. Application March 23, 1954 SerialNo. 418,222

6 Claims. (Cl. 25239) This invention relates to improved calcium basegreases. More particularly it relates to anhydrous calcium hydroxy fattyacid soap greases and to a method of preparing them.

This application is a continuation-in-part of our copending application,Serial No. 388,426, filed October 26, 1953, now abandoned, wherein it isdisclosed that stable anhydrous calcium base greases may be successfullyprepared by employing a hydroxy fatty acid material as the saponifiablematerial and carrying out the preparation by a method which involvessaponification in the presence of a small amount of a naphtheniclubricating oil and dehydration at an elevated temperature above themelting point of the soap. This continuation-impart application involvesthe additional discovery that in order to obtain a grain-free product ofgood marketable appearance it is necessary to employ in thesaponification a hydroxy fatty acid material which contains a minimumamount of estolide polyesters of the hydroxy fatty acid.

Anhydrous calcium hydroxy fatty acid soap greases have been successfullyprepared, as disclosed in the copending application of O. P. Puryear, H.V. Ashburn and J. P. Dilwo-rth, Serial No. 247,558, filed September 20,1951, now abandoned, by a low temperature process wherein thesaponification and subsequent dehydration steps are carried out in aminor portion of the lubricating oil included in the grease at atemperature below the melting point of the soap, and the remainder ofthe lubricating oil added gradually with continuous stirring while themass is allowed to cool. Earlier attempts which were made by Fraser, U.S. 2,380,960, and others to prepare calcium hydroxy fatty acid soapgreases without the use of water or other stabilizing agent, employingthe high temperature-method wherein the soap and the lubricating oil areheated together at a temperature above the melting point of the soapuntil the soap is completely melted, were unsuccessful, separation ofthe oil and soap taking place during the cooling down process.

These anhydrous calcium base greases of Puryear et al. represent aconsiderable advance in the art, since they are free from the seriousobjection of thermal instability due to the loss of water fromwater-stabilized greases at temperatures above about 212F., which hasplaced a. severe limitation upon the usefulness of calcium base greasesin the past.

However, the method of preparation employed by Puryear et al. has thedisadvantage that very careful temperature control is necessary duringthe dehydration step in order to avoid local overheating and partialmelting of the grease mixture, which results in a lumpy andunsatisfactory product. Also, it is difficult to obtain these greasesfree from graininess; and a special technique, involving cold premixingof the reactants in the saponification mass, in addition to closecontrol of the other operating conditions, is used to obtain greases ofmarketable appearance.

We have now found that the above difficulties are 2,882,884 PatentedDec. 2, 1958 avoided and anhydrous calcium base greases of excellentsmoothness and texture are consistently produced by a method whichinvolves saponifying a hydroxy fatty acid material, containing a smallproportion of hydroxy fatty acid estolides, in the presence of a smallamount, equivalent to only a minor proportion of the oleaginous liquidlubricating base employed in the grease, of a naphthenic lubricatingoil, and then dehydrating the mass at a temperature above the meltingpoint of the soap. The temperature at which the dehydration is carriedout will depend somewhat upon the particular calcium hydroxy fatty acidsoap in the saponification mass, but in general it is preferable tocarry out this process at a temperature of atleast about 280300 F.Following the dehydration, additional lubricating oil, sufficient togive a grease of the desired consistency, is added slowly withcontinuous stirring while the mass is allowed to cool. Additives of theusual types may be added during the cooling down process, ordinarilywhen the temperature of the mass is below about 200 F.

The hydroxy fatty acid material employed in the saponification is a soapforming hydroxy fatty acid material selected from the group consistingof hydroxy fatty acids containing at least 12 carbon atoms in themolecule and one or more hydroxy groups, and the glycerides of suchacids. The acids are preferably substantially saturated acids containingfrom 12 to 24 carbon atoms and one or two hydroxy groups, such asmonoand di-hydroxy stearic, oleic, myristic and palmitic acids. Aparticularly suitable material of this character is l2-hydroxy stearicacid. Other acids of this type which may be mentioned include 9- and10-hydroxy stearic acids, 9,10- dihydroxy stearic acid and 8-hydroxypalmitic acid.

The estolides which must be present in the hydroxy fatty acid materialin order to obtain grain-free greases are intermolecular esters andpolyesters formed by the reaction of the hydroxy group of one moleculeof the hydroxy fatty acid with the carboxy group of another. Theestolides of monohydroxy fatty acids containing 12 to 24 carbon atomsare represented by the formula:

wherein R is hydrogen or an aliphatic hydrocarbon radical containingfrom 1 to 21 carbon atoms, x is an integer having a value of 1 to 22 andn is an integer having a value of 2 to about 10. The estolides of12-hydroxy stearic acid are represented by the above formula wherein Ris an alkyl radical containing 6 carbon atoms and x is equal to 10. Thel2-hydroxy stearic acid employed in the grease making suitably containssuch estolides having an average molecular weight in the range fromabout 800 to about 1,200, represented by the above formula wherein n hasa value of 2 to about 5.

The minimum percentage of estolide which must be present in the hydroxyfatty acid material in order to obtain grain-free greases is about 3percent by weight, and is preferably in the range from about 4 to about10 percent by weight, based on the total weight of the hydroxy fattyacid material. Larger amounts of estolides may be present in thesaponifiable material without impairing the properties of the grease,but the presence of such large amounts of estolides has the disadvantageof materially decreasing the yield, and amounts in excess of about 15percent by weight of the fatty acid material are regarded asobjectionable for this reason.

The naphthenic oil employed in the saponification mixture is suitably adistillate fraction in the low or medium viscosity lubricating oilrange, such as an oil having a Saybolt Universal viscosity below about600 seconds at F., and preferably below about 350 seconds at 100 F. Withparticular advantage, it may be very light naphthenic lubricating oilhaving a Saybolt Universal viscosity in the range from about 40 to about200 seconds at 100 F. Suitable proportions of the oil and saponifiablematerial may be from about 0.5 :1 up to about 1' by weight, and arepreferably from about 1:1 to about 3:1 by weight.

The lubricating-oil which is employed for finishing off the grease, andwhich comprises the chief oil component of the grease, may be of thesame type as that employed in the saponification mixture, or a dilferentoil may be employed, such as a paraflinic oil or an oil of higher orlower viscosity. Suitable oils for this purpose include both distillateand residual oils of naphthenic or paraffinic character, havingviscosities in the range from about 50 to about 1,200 seconds SayboltUniversal at 100 F., as well as blends of such oils. Also, other typesof liquid oleaginous lubricating bases can be employed for this purposeeither in whole or in admixture with mineral lubricating oils. Forexample, any of the so-called synthetic lubricant, such as aliphaticdicarboxylic acid esters of the character of Z-ethyl hexyl sebacate, canbe used.

In accordance with our preferred procedure, a saponifiable hydroxy fattyacid material containing 3-15 percent by weight of estolides and anaphthenic oil of the character described above and in the disclosedproportions are charged to a grease kettle together with a small amountof water and lime in the calculated amount for saponifying the fattyacid material, together with a slight excess if desired. The greasekettle may suitably be an open type grease kettle equipped with stirrersand. a steam heating jacket, or a pressure kettle may veryadvantageously be employed. The charge is heated with stirring to aboutISO-210 F., and preferably to about ISO-210 F., under either atmosphericor increased pressure, and maintained at this temperature until thesaponification is substantially complete, which usually requires fromabout 2 to about 4 hours. The temperature is then increased up to abovethe melting point of the soap in the open kettle with continued stirringand held at this temperature for a period sufficient to substantiallydehydrate the mass, which usually requires from about one half up toabout 2 hours or more. The temperature at which the dehydration iscarried out will depend upon the melting point of the soap. For example,when 12-hydroxy fatty acid or a glyceride thereof is employed in thesaponification, the dehydration is suitably carried out at at leastabout 280 F., and preferably at a temperature between about 300 F. andabout 330 F. The dehydrated mass, with.

water content below about 0.2 percent and generally not more than about0.1 percent by weight on the basis of the, final grease, is then broughtto the desired consistency by the addition of the major quantity of theliquid oleaginous lubricating base with continuous stirring as the massslowly cools. The grease is preferably stirred down to about 200 F. orlower, and discharged from the kettle at about 160180 F. by pumping itthrough straining screens in the conventional manner.

In carrying out the oil addition during the cooling down process, atleast a major portion of the oil is preferably added while thesaponified mass is at a temperature below the melting point of the soap.When a hydroxy fatty acid is employed as thesaponifiable material, theoil addition may be started at a temperature above the melting point ofthe soap if desired and continued during the entire cooling downprocess. However, when a hydroxy fatty acid glyceride is employed as thesaponifiable material a difference has been noted in this respect, itbeing necessary for best resultsto cool the saponified mass down to atemperature below the melting point of the soap and to stir until agrease consistency is obtained before starting the oil addition. Forexample, in preparations employing hydrogenated castor oil as thesaponifiable material, it was necessary to cool to about 250 F. and tostir for at least about an hour at that temperature before adding theadditional oil. By employ g t is p caution, very satisfactory greaseshave been prepared according to the method of our invention from hydroxyfatty acid glycerides as the saponifiable material.

According to a modification of the above procedure which may be employedvery advantageously as a means of avoiding difficulties in stirring thestiff soap base at a temperature below the melting point of the soap,all or a portion of the lime required for the saponification may beadded to the mixture of saponifiable hydroxy fatty acid material and oilafter the mixture has been heated to a temperature above the meltingpoint of the soap. Where all or a major portion of the lime is added atsuch higher temperature, the saponification is preferably carried out ina closed kettle under at least moderately elevated pressure. Thedehydration and finishing steps may then be carried out in the openkettle in the manner described above. Preferably, a major portion of thelime required for the saponification is added to the original charge andthe remainder of the lime is added after at least a partial melting ofthe soap has taken place. For example, grease preparations have beencarried out very successfully employing l2-hydroxy stearic acid as thesaponifiable material wherein about three-fourths of the amount of. limerequired for complete saponification was added to the original charge,saponification carried out at 150-2l0 F., and the remainder of the limerequired for completion of the saponification added after the mass washeated to about 270 F.

A particularly valuable application of this invention is found in thepreparation of anhydrous calcium hydroxy fatty acid soap greases fromvery low viscosity oils, such as lubricating oils having viscositiesbelow about seconds Saybolt Universal at 100 F. conventionally, in thepreparation of calcium base greases, the soap is prepared in thepresence of an oil of about 300 seconds Saybolt Universal viscosity at100 F., and oils substantially below about 100 seconds Saybolt Universalviscosity at 100 F. have not been employed for this purpose because ofthe poor solubility of the calcium fatty acid soaps in the very lowviscosity oils and the very poor yields obtained. In order to obtaingreases of satisfactory stability, the use of these light oils incalcium base greases has been limited to only minor amounts which havebeen employed in blends with heavier oils. We have found that, due tothe superior solubility of the calcium hydroxy fatty acid soaps in suchoils, these very light oils can also be employed in the soap preparationaccording to the method of our invention, and very stable anhydrouscalcium base greases can be prepared in excellent yield employing theselight lubricating oils as the chief oil component. A combination of veryvaluable lubricating properties is thereby obtainable which is notobtainable when either higher viscosity oils or the conventional calciumfatty acid soaps are employed, including outstanding low temperatureproperties combined with suitability for use at temperature above 212 F.Also, these greases are highly shear stable and resistant to softeningor other deterioration under conditions of high shearing stress, andgreases of excellent shear stability, suitable for use as wheel bearinglubricants, are obtained with only relatively low amounts of the calciumhydroxy fatty acid soap in these light lubricating oils, such as about,10 percent or less of the soap for a NLGI No. 2 grade grease. We havefound that greases having the difficultly obtainable combination oflubricating properties necessary to meet the requirements of GovernmentSpecification MIL-G-l0924 for a water resistant wide temperature rangeball and roller bearing grease can be produced by employing acombination of a calcium hydroxy fatty acid soap and a very lowviscosity lubricating oil, having a Saybolt Universal viscosity at 100F. below 100 seconds.

Greases of. the above, type may suitably comprise about 5 to 20 percentby weight of a calcium hydroxy fatty acid soap and a mineral lubricatingoil having a viscosity in the range from about 50 to about 100 secondsSaybolt Universal at 100 F. as the oil component. The oil may comprise ablend of lighter and heavier oils, but preferably it contains no morethan a minor proportion, such as less than about 25 per cent by weight,of an oil having a viscosity outside of the viscosity range disclosedabove.

A preferred grease composition of this type comprises about 815 percentby weight of calcium hydroxy fatty acid soap, including calcium soap ofestolides, and a distillate mineral lubricating oil having a SayboltUniversalviscosity at 100 F. of about 50 to about 75 seconds, which maybe a blend of lighter and heavier oils in the viscosity range from about40 to about 100 seconds Saybolt Universal at 100 F., as the oilcomponent. The grease preferably contains a small amount of freealkalinity, suitably about 0.05 to about 0.5 percent by weight,calculated as Ca(OH) A small amount of free fatty acid, such as up toabout 0.3 percent by weight may also be present, although this is notnecessary for imparting stability or other desired lubricatingproperties to the grease.

Additives of conventional type may be employed, such as extreme pressureagents, pour depressants, oxidation inhibitors, corrosion inhibitors,dyes and the like. Preferably, the grease contains both a corrosioninhibitor and an oxidation inhibitor, oxidation inhibitors of the aminetype, such as diphenylamine, alphaand beta-naphthylamines and N,Ndiphenyl para phenylenediamine being especially suitable. A particularlyeffective additive combination of this type has been found to comprisesorbitan monooleate, which may be suitably employed in amounts of about1-5 percent by weight of the grease, and a commercial oxidationinhibitor (Ortholeum 300) consisting of 95 percent diphenylamine and 5percent salicylalamino-guanidine oleate, which may suitably be employedin amounts of about 0.1-1.0 percent by weight of the grease. Inaddition, a small amount, such as about 0.2-2 percent by weight, of aManvel residuum (residual oil from Manvel crude) having a SayboltUniversal viscosity of about 600-800 seconds at 210 F. may veryadvantageously be employed in order to impart a desirable green color tothe grease.

A number of anhydrous greases of the above type were prepared verysuccessfully in both laboratory and plant size batches according to themethod of this invention from hydroxy fatty acid materials, employinglight naphthenic distillate oils having viscosities from about 40 toabout 100 seconds Saybolt Universal at 100 F. in the kettle charge andfinishing by blending in oils of the same or diiferent types, such asparaffinic oils and oils of different viscosities within the aboverange. In every case the preparation proceeded without separation of thesoap and oil during the finishing process or other difficulties andgreases of good stability and other lubricating properties wereobtained. In addition, greases which were entirely free from graininesswere obtained when hydroxy fatty acid materials containing at least 3percent by weight of estolides were employed in the saponification;

The preparation of a grease of a preferred type in accordance with thisinvention is described in detail in Example 3 below. Example 1 isrepresentative of unsuccessful attempts which were made previously toprepare anhydrous calcium hydroxy fatty acid greases, and shows thecriticality of employing a naphthenic type oil in the saponification anddehydration steps. Example 2 is representative of greases prepared inaccordance with the method of this invention but employing estolide-freehydroxy fatty acid materials.

EXAMPLE 1 An open typelaboratory grease kettle equipped with stirrersand a steam heating jacket was charged with 9 pounds of distillateparafiin base mineral lubricating oil of SAE 20 grade having a SayboltUniversal viscosity at 100 F. of 325 seconds, 9 pounds of Hydrofol acids200, 6.5 pounds of water and 605 grams of dry powdered lime. Hydrofolacids 200 is a product of the Archer Daniels Midland 00., comprising inmajor proportion 12-hydroxy stearic acid and containing approximately 5percent of 12-hydroxy stearic acid estolides having an average molecularweight of about 1,000. The material employed in this preparation had aneutralization number of 174, a saponification number of 187, and iodinenumber of 3, a titer, C. of 74.7 and a hydroxyl number of 148. Thekettle contents were heated with stirring to about 185197 F. andmaintained at that temperature for 4 hours to obtain completesaponification. The heat was then increased and the temperature of thesaponified mass brought up to about 300 F. in about 1.3 hours, andmaintained at 308-320 F. for about 1.1 hours longer to dehydrate. Themass was then allowed to cool gradually while it was attempted to stirin additional mineral oil of the same type as that employed in theoriginal charge. However, the mass rejected oil starting at about 275 F.and broke completely into soap lumps and free oil at about 250 F. Thegrease was finally stirred down to 200 F. before the oil addition wascarried out, in an attempt to smooth out the soap base. An extremelylumpy and grainy product was finally obtained in a very poor yield, 19.9percent of the calcium 12-hydroxy stearate being required to give anumber 2 grade grease, having an ASTM worked penetration at 77 F. of298.

EXAMPLE 2 The grease preparation was carried out in substantially thesame manner as described in Example 1, except that a naphthenicdistillate oil was employed, having a Saybolt Universal viscosity at 100F. of 59.4, a flash point, COC, of 305 F. and a pour point of -55 F.Also, a 12-hydroxy stearic acid was employed which was free fromestolides, as indicated by its hexane insolubility at 32 F. Thismaterial had a neutralization number of 180, a saponification number of186 and a hydroxyl number of 161. The kettle was charged with 14.0pounds of the lubricating oil, 14.1 pounds of the 12 hydroxy stearicacid, 10.0 pounds of water and 964 grams of dry powdered lime. Thecharge was heated with stirring to 182-194 F., and maintained at thistemperature for 4 hours to complete the saponification. The temperatureof the saponified mass was then brought up to about 308 F. in about 2.5hours and maintained at 308322 F. for an additional 2.2 hours todehydrate. The heat was then cut off and additional lubricating oil ofthe same type as that employed in the original charge was mixed in withcontinuous stirring while the mass cooled from about 322 F. to about 120F. during about 20 hours. When the grease was at about 200 F., 4.1pounds of sorbitan monooleate (Span and 0.69 pound of Ortholeum 300,dissolved in a part of the lubricating oil, were added. About 1.4 poundsof Manvel residuum having a Saybolt Universal viscosity of 731 secondsat 210 F. were also mixed in at this tempera ture. The grease wasfinally drawn from the kettle at about F. and pumped through three60-mesh screens.

No separation of the oil and soap or lump formation occurred during theabove process, and a grease was obtained having a dropping point of 286and a worked penetration at 77 F. of 283 for a soap content of 10.8percent. However, the grease was very grainy and clogged the screensduring the screening process.

EXAMPLE 3 as described in Example 2, and an estolide-containing12-hydroxy stearic acid of the same character as described in Example 1(Hydrofol acids 200). The kettle was charged with 9.43 pounds of thelubricating oil, 9.43 pounds of the estolide-containing 12-hydroxystearic acid, 6.5 pounds of water and 629 grams of dry powdered lime.The charge was heated with stirring to 182-197 F., and maintained atthis temperature for 4 hours to complete the saponification. Thetemperature of the saponified mass was then brought up to about 300 F.in about 1.3 hours and maintained at 303-309 F. for an additional 0.5hour to dehydrate. The heat was then cut off and additional lubricatingoil of the same type as that employed in the original charge was mixedin with continuous stirring while the mass cooled from about 309 F. toabout 176 F. during about 12 hours. When the grease was at about 190-200F., 1352.5 grams of sorbitan monooleate (Span 80) and 227.3 grams ofOrtholeum 300, dissolved in a part of the lubricating oil, were added.About 450.8 grams of Manvel residuum having a Saybolt Universalviscosity of 731 seconds at 210 F. were also mixed in at thistemperature. The grease was finally drawn from the kettle at about 170F. and pumped through three 60-mesh screens.

No difficulties of any kind were encountered in this preparation and asmooth glossy buttery product was obtained in excellent yield. Thefollowing Table I shows the composition and tests on this grease.

Table I having an SUS viscosity at 100F. of about 60. sorbitanmonooleate Ortholeum 300" Manvel residuum.

ests:

Water Free alkali, as Ca(H)z.. Free fatty acid, as oleic. Droppin point,F ASTM penetration at 77 F;

Unworked 242 310 max.

Worked 290 350 max. Apparent viscosity Tcst,65 F

25 see- 10,050 10,000 mm.-

100 sec.'.

500 sec.

Evapration Test, ASTM-D-972, 22 hrs.

at 210F., percent loss.

Oil Bleeding Test, 50 hrs. at 160 F., 0 40max percent loss.

Bomb Copper Corrosion Test, 20 hrs.

at 210 F.:

Copper Clean Light brown,

max.

Grease Slight dis- Slight change,

coloration. max.

Rating Pass Must pass. Salt Spray Trst, 100 hrs., percent rust.. 0 Norust. Wheel Bearing Test, a. leakage 3 max. Norma-Hofirnann OxidationTest:

P. s. i. drop- 100 hrs 3 5 lb. max/100 hrs. for 400 hrs.

100-200 hrs max.

All of the tests listed in the above table were carried out inaccordance with the methods prescribed by specification MIL-G-10924.

'The apparent viscosity test is a test indicating the suitability of agrease for use at very low temperatures, and is carried out by forcingthe grease, at a temperature of --65 F.- -0.5 F., through a series ofcapillaries of different sizes by means of a floating piston actuated bya hydraulic system, at shear rates of 25, 100 and 500 reciprocalseconds. The apparent viscosity is calculated from the predeterminedflow rate and the force developed in the system. As shown by the table,the grease of Example 3 very satisfactorily met these low temperaturerequirements of the specification.

The bomb copper corrosion test is carried out by placing a cleaned andpolished strip of electrolytic copper (1.75 x 0.25 x 0.02 inch in sizeand bent to a V-shape) on edge in a /s inch layer of the test grease ina glass dish and placing the dish in a Norma-Hoffman oxidation bomb for20 hours at 210 F. and 110 p. s. i. After the test the copper strip andthe grease are examined for discoloration. As shown by the table, thegrease of Example 3 met the oxidation and corrosion resistancerequirements of this rigorous test.

The salt spray test is a test commonly employed to show the rustresisting properties of greases under conditions of high humidity and inthe presence of rust accelerating salts such as are present in seawater. The test is carried out by thinly coating steel panels with thetest grease and maintaining them in contact with a spray of syntheticsea water, containing sodium, calcium and magnesium chlorides and sodiumsulfate, at a temperature of F. and atmospheric pressure for hours. Asrequired by the specification, the grease of Example 3 permitted norusting of the panels during 100 hours exposure to the severe rustingconditions of this test.

The wheel hearing test is a test indicating the ability of a grease tomaintain satisfactory lubrication without undue softening or otherdeterioration at elevated temperatures and high shearing rates underservice conditions. The test is carried out as described in OrdnanceDepartment Specification AXS-1574 by packing a front wheel hub andspindle assembly with 90 grams of the test grease and rotating the wheelfor 6 hours at a speed of 430-450 R. P. M. and at a spindle temperatureof 220 F. At the end of the run, the condition of the bearing parts andthe appearance of the grease are noted and the amount of leakage isdetermined by weighing the grease or oil collected in a retainer at theback of the hub. The grease of Example 3 passed this test verysatisfactorily, excellent lubrication being maintained with no more thanslight deterioration of the grease and with only a small amount ofleakage as shown by the table.

The Norma-Hoffmann oxidation test is a well-known test for measuring theresistance to oxidation of a lubricating grease when stored under staticconditions for long periods of time. Samples of the grease are tested ina stainless steel bomb sealed in an'atmosphere of oxygen under initialpressure of p. s. i. at 210 F., with the pressure drop at the end of 100hours being recorded. A grease giving a pressure drop of less than 5 p.s. i. per hundred hours up to 400 hours in this test is generallyconsidered to have excellent oxidation resistance properties.

As shown by the data given in the table, the grease of Example 3,representative of the preferred greases of our invention, had thecombination of exceptional low temperature properties and goodlubricating properties at elevated temperatures, includingsatisfactorily low evaporation loss, stability, and excellent oxidationand corrosion resistance, necessary to meet the difficult requirementsof specification MILG-19924. Other tests not listed have also shown thisgrease to have excellent resistance to softening and oil separation uponsevere working and resistance to change upon working in the presence ofwater.

In addition to the above tests, greases of substantially the samecomposition as the grease of Example 3 have been tested verysuccessfully as wheel bearing lubricants in actual service tests carriedout under severe conditions, including extreme atmospheric temperaturesand the presence of water. For example, a grease of this compositiongave very outstanding performance as a wheel bearing grease in a10,000-mile test in Army trucks carried out in the California desert, atan ambient temperature ranging from 85 F. to 120 F. and hub temperaturesas high as 233 F. developed under the severe braking employed. At theend of this test the grease appeared to be unchanged in consistency, thebearings being well lubricated and in good condition and no leakagehaving occurred from the hubs.

While the method of this invention is of particular utility in theproduction of stable anhydrous calcium base greases, as discussed above,it is understood that other alkaline earth metal soap greases also mayadvantageously be prepared by this method, such as, for example, bariuml2-hydroxy stearate grease, strontium 12-hydroxy stearate grease, barium-hydroxy myristate grease, strontium l2-hydroxy oleate grease, barium9-hydroxy stearate grease and strontium IO-hydroxy stearate grease. Thepresence of the prescribed amount of estolide in the hydroxy fatty acidmaterial employed in the saponification is also critical in theproduction of such other alkaline earth hydroxy fatty acid greases toobtain greases of superior smoothness.

Mixed base greases containing hydroxy fatty acid soaps of two or moredifferent alkaline earth metals or a major proportion of an alkalineearth metal hydroxy fatty acid soap with a minor proportion of an alkalimetal hydroxy fatty acid soap are included in the present inventionwhere the type and proportion of the other soap mixed with the majorproportion of the alkaline earth metal hydroxy fatty acid soap does notseriously impair the advantageous properties obtained with the straightalkaline earth metal hydroxy fatty acid soap grease. For example,greases of higher dropping points have been obtained without substantialsacrifice of water resistance or other desirable properties of thesegreases by employing a soap containing about 10 percent by weight ofsodium hydroxy fatty acid soap based on the total soap in addition tocalcium hydroxy fatty acid soap.

Obviously, many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

We claim:

1. The process of preparing a stable substantially anhydrous calciumbase lubricating grease which comprises saponifying a hydroxy fatty acidmaterial selected from the group consisting of substantially saturatedmonoand dihydroxy fatty acids containing from about 12 to about 24carbon atoms, and the glycerides thereof, with calcium hydroxide in thepresence of a small amount equivalent to only a minor proportion of theliquid oleaginous lubricating base employed in the grease of anaphthenic distillate lubricating oil having a viscosity in the rangefrom about 40 to about 600 seconds Saybolt Universal at F., heating thesaponified mass at a temperature above the melting point of the soap fora time sufiicient to substantially dehydrate the said mass, andthereafter gradually adding additional lubricating oil with continuousstirring as the said mass is cooled at a temperature below the meltingpoint of the said soap, said hydroxy fatty acid material containing 315percent by weight of estolides having an average molecular weight inabout the range 800-1200.

2. The process of claim 1 wherein the said naphthenic distillatelubricating oil, and the said hydroxy fatty acid are employed in thesaponification in a proportion between about 05:1 and about 5:1 byweight.

3. The process of claim 1 wherein the said naphthenic distillatelubricating oil is an oil having a viscosity in the range from about 40to about 200 seconds Saybolt Universal at 100 F.

4. The process of claim 1 wherein the said hydroxy fatty acid materialis 12-hydroxy stearic acid.

5. The process of preparing a stable substantially anhydrous calciumbase lubricating grease which comprises saponifying 12-hydroxy stearicacid with lime at 15 0210 F. in the presence of about 0.5 to about 5times the quantity of a naphthenic distillate lubricating oil having aviscosity in the range from about 40 to about 100 seconds SayboltUniversal at 100 F., heating the saponified mass at a temperature fromabout 280 F. to about 330 F. for a time suflicient to substantiallydehydrate the said mass, and thereafter gradually adding additionallubricating oil with continuous stirring as the said mass is cooled downto about 200 F., said 12-hydroxy stearic acid containing 4-10 percent byweight of estolides having an average molecular weight in about therange 8001200.

6. The process of claim 5 wherein the 12-hydroxy stearic acid is reactedat ISO-210 F. with a major portion of the lime required for thesaponification and the remainder of the lime required is added to thesaponification mass at a temperature about 270 F.

References Cited in the file of this patent UNITED STATES PATENTS2,588,556 Moore et al Mar. 11, 1952 2,607,734 Sproule et al Aug. 19,1952 2,607,735 Sproule et al Aug. 19, 1952 2,613,182 Sproule et al. Oct.7, 1952, 2,618,599 King et a1 Nov. 18, 1952 2,625,510 Moore Jan. 13,1953 2,648,634 Moore Aug. 11, 1953 2,652,365 Moore et al. Sept. 15, 19532,652,366 Jones et al. Sept. 15, 1953 2,695,878 Entwistle Nov. 30, 1954

1. THE PROCESS OF PREPARING A STABLE SUBSTANTIALLY ANHYDROUS CALCIUMBASE LUBRICATING GREASE WHICH COMPRISES SAOINIFYING A HYDROXY FATTY ACIDMATERIAL SELECTED FROM THE GROUP CONSISTING OF SUSBSTANTIALLY SATURATEDMONO-AND DIHYDROXY FATTY ACODS CONTAINING FOM ABOUT 12 TO ABOUT 24CARBOB ATOMS, AND THE GLYCERIDES THEREOF, WITH CALCIUM HYDROXIDE IN THEPRESENCE OF A SMALL AMOUNT EQUIVALENT TO ONLY A MINOR PROPORTION OF THELIQUID OLEAGINOUS LUBRICATING BASE EMPLOYED IN THE GREASE OF ANAPHTJENIC DISTILLATE LUBRICATING OIL HAVING A VISCOSITY IN THE RANGEFROM ABOUT 40 TO ABOUT 600 SECONDS SAYBOLT UNIVERSAL AT 100*F., HEATINGTHE SAPONIFIED MASS AT A TEMPERATURE ABOVE THE MELTING POINT OF THE SOAPFOR A TIME SUFFICIENT TO SUBSTANTIALLY DEHYDRATE THE SAID MASS, ANDTHEREAFTER GRADUALLY ADDING ADDITIONAL LUBRICATING OIL WITH CONTINOUSSTIRRING AS THE SAID MASS IS COOLED AT A TEMPERATURE BELOW THE MELTINGPOINT OF THE SAID SOAP, SAID HYDROXY FATTY ACID MATERIAL CONTAINING 3-15PERCENT BY WEIGHT OF ESTOLIDES HAVING AB AVERAGE MOLECULAR WEIGHT INABOUT THE RANGE 800-1200.